104 



TUNICATA. 



surface. The mouth has usually the form of a broad transverse slit, 

 bounded by movable lips, and leads into the large respiratory 

 cavity, which consists of the pharyngeal cavity and the cloaca, and 

 contains the lamellar or band-shaped gill, extended from the dorsal 

 surface obliquely backwards and ventralwards. In Doliolum the 

 gill has the form of an oblique partition, which is pierced by two 

 lateral rows of large transverse slits, through which the water flows 



FIG 566. Salpa mucronata. b, S. democratica. 0, Mouth ; A, cloacal aperture ; N, ganglion; 

 r, gill End, endostyle ; Wg, ciliated pit ; Ma, mantle ; Nu, nucleus ; C, heart ; 

 Emb, embryo ; Stp, stolo prolifer. 



from the pharyngeal cavity into the cloacal chamber. In Salpa the 

 transverse slits are represented by one very large gill-slit on each 

 side, so that the branchial wall is reduced to a median band (the 

 median part of the gill of Doliolum). The two arches of cilia which 

 bound the entrance to the respiratory cavity, and the ventral endo- 

 style (mucous gland) from which a ciliated groove leads to the 

 oesophagus, are placed in the wall of the pharyngeal cavity. 



